Loud speaker



Patented ct. 2K0, 1931 UNITED STATESA PATENT OFFICE :rorm rar-.cronmrow, or WHITE nuns, NEW Yonx, AssrG'NoE 'ro amro con.- romrroN orAMERICA, A conPoaA'rroN or Enawm LOUD ySPEAKER plantation-med :une 1s,m8. serial No. sans.'

The invention relates to devices for producing sounds by electriccurrent and has for its principal object to improve the quality ofsounds emitted and to increase the intensity {5} thereof. Amore-specificobject of the invention is to provide an acoustic ldevice from whichsounds will be emittedfrom the front part'of the diaphragm onl y,

Still another object of t e invention is to "'4 provide an acousticAdevice in which the sound will be emitted from the front part of thediaphragm only, any tendency to interference between sound waves fromthe front and l `rear of the diaphragm being overcome.

.15j It .is Well known' that the construction of man types of acousticdevices of the loud spea er typ? forms a fairly large cavity behind thev1 rating diaphragm and it is often necessary or desirable to enclose'this cavity by the casing of the device., This closed cavity has'certain undesirable effects on the intensity and quality of soundemitted for several reasons.' In the rst place under certainAyconditions sound energy may flow from both sidesot the diaphragmthereby theoretically at least, reducing by one half the' useful soundenergy, as of course, ordinarily only the sounds emitted b the frontpart of the diaphragm are use ul.' Another bad eiect of such a closedcavity may be traced to the casing itself which may have sufficientresiliency to cause it to vibrate in sympathy with the vibrating lcolumnof air entrapped in it. This will give the effect of a second soundsource and sound waves'from it will naturallfy interfere more or lesswith. waves emitted omthe front part of thediaphra therecausingdistortion and lessened intensity. Still another eifect'resides in theaction of the vibrating column of air on the diaphra itself. The columnof air set in motion y therear face of the diaphra will of course bereflected by the walls of t e enclosing casing and there will be certainfrequencies at which strong resonant effects willbe obtained therebyincreasing the amplitude of the diaphragm vibrations. At certain otherfrel quencies the entrapped air inthe casing may be reflected in thecorrect phase relationship `to exactly oppose the vibration of thediawith a modified form of lining.

phra m, thereby cuttin down its amplitude of v1 ration considerab y.While these effects are more noticeable at certain frequencies than atothers it is obvious that they will 4waves from the rear of thediaphragm being reflected from the Walls of the casing and therefore, notendency to resonant edects. This material also, if properly chosen,will prevent the passage of sound waves through it and, therefore,obviate any tendency of the casing itself to vibrate. The sound emittedby the device so constructed will, therefore be free from distortion andgreatly increas in intensity, giving a faithful loud reproduc-` tion ofthe original sound.

The invention is illustrated, by way of example, in the accompanyingdrawings in whichv Fig. 1 illustrates the operating mechanism of a loudspeaker constructed in accordance with the invention.

Fig. 2 is a sectional view on line 2-2 of Fig. 1 showing theconstruction of the lined .casing Wall, and

Fig. 3 is a cross section of a casing Wall Referring to Fig. 1, theoperating mechanism of a loud speaker of a Well known type isshowncomprlsing a base 1 on which is mounted a support 6, to which isfastened the operating mechanism of the loud speaker. The operatingmechanism comprises a permarient magnet 3, held in place on'the support6 by the clamp 5. The vibrating armature 7 isl suitabl supported asshown and the o eratino' coi 4 is mounted on the armature and foastenedto the vibratory cone 9 100 by means of the r'od' 8.' The cone 9 hasiianges provided at its outer ed e which are fixedto flexible ring 10,clampe in place bctween the clampin rings 11. The outer or operativesurface o the cone 9 communlcates with the sound duct l2 which may bejoined 49 will' then, of course, reproduce the sounds which originallycaused the undulations of current in the, coil 4.

The undesirable effects noted above are obviated in the device shown inthe igure bg lining the cavity behind the diaphragm Wit sound absorbingmaterial shown at 13. This, as pointed out above, prevents any resonanteffects due to the presence of the closed chamber and also prevents anyvibration of the casing 2, permitting it to act as a secondary soundsource.

It has been found that a felt lining as shown in Fig. 2 will eliminateall the undesirable eiects but in order to obtain substantially perfectoperation of the diaphragm, this felt would have to be of considerablethickness, probably an inch, which ordinarily would make the apparatustoo bulky. It should' be noted however, that a much thinner lining offelt or absorbing material will substantially improve the operation ofthe device and it is not always necessaiy to make a covering of thisthickness.

ig. 3 shows a modication of a lining for the casing which is not undulybulky and which gives substantially the same results as a felt lining aninch thick. The shown in Fi re 3 comprises a layer of le foil 202 whichis attached to the casing 201, and a layer of felt 203 which covers thelayer of lead foil. rI`he layer of lead foil may be about 5 mils thickand the layer of felt may be about l; of an inch thick. It has beenfound that this gives substantially perfect operation of the device froman acoustical point'of view and that it is rnot so bulky as to make itobjectionable from the manufacturing standpoint. The lead foil in thiscase forms a substantial rigid barrier which transmits and reflectssound waves ve rly, if at all, thereby making a thif ligger of feltunnecessary.

The device is illustrated and described in connection with a loudspeaker having a completely enclosed cavity behind its diap and this isthe application in which the inveneiects which it is' designed toprevent.

tion is most effective and will nd its use as, in this case theundesirable e'ects pointed out above will be at their maxima. Thedevice, however, is not limited to this specific case' as it can beequally well a p lied to 70 a cavity behind the diaphra whic is onlypartially enclosed and coul even be applied to an 'open diaphragm inwhich objects in the vicinity would tend to cause any ofthe While I haveshown the device in several very specific modifications, it is obviousthat many other methods of puttin it into effect will readily occur tothose ski ed'in the art'. The modications described should therefore betaken in an exemplary andv not in a limitin sense as I intend to belimited only as in icated by the scope of the -following claims.

I claim:

l. An acoustic device comprising a sound emitting element, operatingmechanism and supporting means therefor and a covering comprising alayer of non-vibratory metallic material and a layerof sound absorbingmaterial on said supporting means.

2: An acoustic device comprising a sound emitting element, operatingmechanism and supporting structure therefor and a covering comprising alayer of lead and a layer of kfelt f on said supporting structure.

3. An acoustic device comprising a vibratile element, a casing enclosingthe s ace at the rear of said element and a lining or said casingcomprising a layer of non-vibrator? `metallic material and a layer ofsound absorbing material.

4. An acoustic device comprising a vibratile element, a casing enclosinthe s ao'e at the rear of said element and a ming or saidC casingcomprising a layer of lead and a layer of felt. l

5,. An acoustic device com rising a vibratile diaphragm,a casing encosing the space at the rear of said diaphragm anda soundabsorbing liningfor said casm 6. An acoustic device comprisin a vibratile diaphragm,means formin a su antially enclosed air space in bac of said diaphragm,and a layer of fibrous material positioned in said' enclosed air spacefor reducing the 'damping action of the entrapped air on said diaphragm.

. 7.- An acoustic device comprising a vibratile diaphragm, means forpreventing com- "12 f munication between the rear and the front of saiddiaphragm, and additional means positione'd at the rear of said diaphrafor'preventin the sound waves radi from the rear o said diaphragm 'fromsubstantially '125 affecting said dia hragm, said additional meansconsisting o a layer of fibrous sound absorbing material. 8. An'acoustic device com rising a vibratile diaphragm, a casing en sing thespace 43.,

saam

at the rear of said dia h and forming a substantially closed all!)lprgt, and acoustic damping material positioned in said air ace forpreventin the sound waves radiated gom the rear of sald diaphragm intosaid substantially closed air pocket from applying a damping action tosaid diaphragm, said acoustic damping means comprising a layer of feltapplied to at least la substantial portion of said casin v 9. Anacoustic evice comprising: conical diaphragm, supporting means at e edgeof said diaphragm, a structure to which said supporting means isattached, said structure forming with said supporting means and saiddiaphragm a substantially enclosed air space, and damping materialpositioned within said air space for reducing the reaction of the entraped air in said air space against said 20. diaragni,fsaid-dampingmateria1"consist:

ing of a: layer of fibrous material secured in back of said diaphragm.

10. An acoustic device com rising a vibratile diaphragm, a casing suantiall 'enclosing the space at the rear of sai diaphragm, means forsecuring said diaphragm to and directly mounting said diaphragm inl saidcasin and vibration dampingmaterial positione within the enclosed space.

3 11. An acoustic device comprisin a conical diaphragm, structuresubstantial y encompassing the rear of said conical diaphragm, and alayer of sound absorbing materlal positioned within said structure.

12. An acoustic device comprising a conical diaphra m, structureencompassing the rear of said iaphragm, and a layer of felt within saidstructure.`

JOHN PRESTON MINTON. c

